1. Field of the Invention;
The invention relates to a process for producing stainless steel based on chromium ore and nickel ore in several process steps coordinated via the intermediate products ferrochromium and ferronickel.
2. Description of the Prior Art.
The process lines for stainless steel established so far worldwide almost exclusively comprise a combination of EAF-AOD-L (duplex process) or EAF-AOD-L (MRP-L)-VOD (triplex process).
The EAF use is different depending upon scrap iron availability or scrap iron and pig iron availability. Presently, the development of the process goes in the direction of using pig iron or liquid chromium together with a reduced portion of low-alloy or high-alloy scrap iron, combined with alloys.
The largest portion among the alloying elements forms chromium and nickel. Nickel is the priciest component. Limited resources of nickel due to the constantly growing final consumer market and, for this reason, the world production are the main reasons for the growing demand for nickel and, for this reason, the growing nickel prices.
New technologies are wanted in order to make the steel material price cost-effective.
In EP 1 641 946 B1, a process for producing an alloyed fused metal is proposed, with the goal to minimize the production costs with high quality and return waste such as Cr- containing or Cr- and Ni- containing dust and slags to the manufacturing process. The process comprises the following process steps, which are performed successively in different converters with top blowing and submerged blowing, in each process step, liquid pig iron from a pig iron mixer being charged into the respective converter:
1. Process step: producing a pre-alloyed melt with 20.3% of Cr and 2% of Ni and a temperature of 1560° C. in a recycling converter.
2. Process step: introducing a Cr carrier and an additional reducing agent, a slag-forming agent, and a fossil fuel into the first pre-alloyed molten charge in a KMS-S converter and producing an alloyed pre-melt for the third process step with 25.9% of Cr and 1.38% of Ni and a temperature of 1500° C.
3. Process step: final treatment in a K-OBM-S converter with addition of in particular ferro-alloys and performance of a decarburization process and adjustment of an alloyed steel melt with the pre-determined chemical analysis of 18.14% of Cr and 8.06% of Ni and a pre-determined temperature of 1860° C.
Another technology for producing high-grade steel is described in U.S. Pat. No. 5,514,331. In this process, the following process steps with the following exemplary results are performed:                producing liquid ferrochromium with a content of 52% of Cr in an arc furnace;        charging the liquid ferrochromium into a ferrochromium converter, in which molten steel with a chromium content of 35% is produced by adding lumpy carbon steel scrap;        filling this steel melt into a transfer ladle and adding a second steel melt charge that is smelted in another arc furnace with a content of 13% of nickel and some chromium;        filling the mixed melt, which is contained in the transfer ladle and has a content of 19% of Cr and 6.6% of Ni, into an AOD converter, wherein finally an end product having a content of 18% of Cr and 8% of Ni is produced.        
Proceeding from the described prior art with the procedures for producing stainless steel with the alloying elements chromium and nickel known so far, it is the object of the invention to show a method, which allows a significant reduction of the steel production costs by directly utilizing chromium ore and nickel ore.